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Register a new userA Pilot Survey of HI in Field Galaxies at Redshift z~0.2
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We present the first results of a targeted survey carried out with the 305 m Arecibo telescope to detect HI-line emission from galaxies at redshift z>0.16. The targets, selected from the Sloan Digital Sky Survey database, are non-interacting disk galaxies in relatively isolated fields. We present here the HI spectra and derived HI parameters for ten objects detected in this pilot program. All are massive disk galaxies in the redshift interval 0.17-0.25 (i.e. 2-3 Gyr look-back time), with HI masses M_HI=3-8 x 10^10 Msun and high gas mass fractions (HI - to - stellar mass ratios ~10-30%). Our results demonstrate the efficacy of exploiting Arecibos large collecting area to measure the HI mass and rotational velocity of galaxies above redshift z=0.2. In particular, this sample includes the highest redshift detections of HI emission from individual galaxies made to date. Extension of this pilot program will allow us to study the HI properties of field galaxies at cosmological distances, thus complementing ongoing radio synthesis observations of cluster samples at z~0.2.
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We present the results of the HIGHz Arecibo survey, which measured the HI content of 39 galaxies at redshift $z>0.16$ selected from the Sloan Digital Sky Survey. These are all actively star-forming, disk-dominated systems in relatively isolated environments, with stellar and HI masses larger than $10^{10}$ M$_odot$ and redshifts $0.17leq zleq 0.25$. Our sample includes not only the highest-redshift detections of HI emission from individual galaxies to date, but also some of the most HI-massive systems known. Despite being exceptionally large, the HI reservoirs of these galaxies are consistent with what is expected from their ultraviolet and optical properties. This, and the fact that the galaxies lie on the baryonic Tully-Fisher relation, suggests that HIGHz systems are rare, scaled-
We measure the neutral atomic hydrogen (HI) gas content of field galaxies at intermediate redshifts of z ~ 0.1 and z ~ 0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope (WSRT). In order to make high signal-to-noise ratio detections, an HI signal stacking technique is applied: HI emission spectra from multiple galaxies, optically selected by the CNOC2 redshift survey project, are co-added to measure the average HI mass of galaxies in the two redshift bins. We calculate the cosmic HI gas densities ({Omega}_{HI}) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the HI gas density over cosmic time. From a total of 59 galaxies at z ~ 0.1 we find {Omega}_{HI} = (0.33 $pm$ 0.05) ~ $times$ 10$^{-3}$, and at z ~ 0.2 we find {Omega}_{HI} = (0.34 $pm$ 0.09) ~ $times$ 10$^{-3}$, based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman-$alpha$ observations and blind 21-cm surveys at $z=$ 0. We find that our measurements of {Omega}_{HI} at z ~ 0.1 and 0.2 are consistent with the HI gas density at z ~ 0 and that all measurements of {Omega}_{HI} from 21-cm emission observations at $z la$ ~ 0.2 are in agreement with no evolution of the HI gas content in galaxies during the last 2.4 Gyr.
High-resolution 21-cm HI deep fields provide spatially and kinematically resolved neutral gas maps at different redshifts, which are key to understanding galaxy evolution across cosmic time and testing predictions of cosmological simulations. Here we present results from a pilot for the COSMOS HI Large Extragalactic Survey (CHILES) done with the Karl G. Jansky Very Large Array (VLA). We take advantage of the newly expanded capabilities of the telescope to probe the redshift interval 0<z<0.193 in one observation. We observe the COSMOS field for 50 hours, which contains 413 galaxies with optical spectroscopic redshifts in the imaged field of view of 34 x 34 and the observed redshift interval. We have detected neutral hydrogen gas in 33 galaxies in different environments spanning the probed redshift range, including three without a previously known spectroscopic redshift. The detections have a range of HI and stellar masses, indicating the diversity of galaxies we are probing. We discuss the observations, data reduction, results and highlight interesting detections. We find that the VLAs B-array is the ideal configuration for HI deep fields since its long spacings mitigate RFI. This pilot shows that the VLA is ready to carry out such a survey, and serves as a test for future HI deep fields planned with other SKA pathfinders.
Using the Hubble Space Telescope/Advanced Camera for Surveys data in the COSMOS field, we systematically searched clumpy galaxies at 0.2<z<1.0 and investigated the fraction of clumpy galaxies and its evolution as a function of stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction of clumpy galaxies in star-forming galaxies with Mstar > 10^9.5 Msun decreases with time from ~0.35 at 0.8<z<1.0 to ~0.05 at 0.2<z<0.4 irrespective of the stellar mass, although the fraction tends to be slightly lower for massive galaxies with Mstar > 10^10.5 Msun at each redshift. On the other hand, the fraction of clumpy galaxies increases with increasing both SFR and SSFR in all the redshift ranges we investigated. In particular, we found that the SSFR dependences of the fractions are similar among galaxies with different stellar masses, and the fraction at a given SSFR does not depend on the stellar mass in each redshift bin. The evolution of the fraction of clumpy galaxies from z~0.9 to z~0.3 seems to be explained by such SSFR dependence of the fraction and the evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also appears to decrease with time, but this can be due to the effect of the morphological K-correction. We suggest that these results are understood by the gravitational fragmentation model for the formation of giant clumps in disk galaxies, where the gas mass fraction is a crucial parameter.
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